U.S. patent number 6,413,255 [Application Number 09/522,275] was granted by the patent office on 2002-07-02 for apparatus and method for treatment of tissue.
This patent grant is currently assigned to Thermage, Inc.. Invention is credited to Roger A. Stern.
United States Patent |
6,413,255 |
Stern |
July 2, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus and method for treatment of tissue
Abstract
An apparatus to treat the skin includes a template having a
tissue interface surface and an energy delivery device coupled to
the template. The energy delivery device is configured to be
coupled to a power source and has a variable resistance portion. A
sensor is coupled to one of the template, the energy delivery
device, the tissue interface surface or a power source coupled to
the energy delivery device. In another embodiment the variable
resistance portion configured to reduce an electrode edge
effect
Inventors: |
Stern; Roger A. (Cupertino,
CA) |
Assignee: |
Thermage, Inc. (Hayward,
CA)
|
Family
ID: |
22408703 |
Appl.
No.: |
09/522,275 |
Filed: |
March 9, 2000 |
Current U.S.
Class: |
606/41; 607/101;
607/102; 607/108; 607/145 |
Current CPC
Class: |
A61B
18/14 (20130101); A61N 1/403 (20130101); A61N
5/04 (20130101); A61B 18/1402 (20130101); A61B
2018/00011 (20130101); A61B 2018/00023 (20130101); A61B
2018/00452 (20130101); A61B 2018/00702 (20130101); A61B
2018/00779 (20130101); A61B 2018/00791 (20130101); A61B
2018/00875 (20130101); A61B 2018/1495 (20130101); A61B
2018/00464 (20130101); A61B 2090/064 (20160201) |
Current International
Class: |
A61B
18/14 (20060101); A61N 1/40 (20060101); A61N
5/02 (20060101); A61N 5/04 (20060101); A61B
19/00 (20060101); A61B 018/18 () |
Field of
Search: |
;606/41,42,50,48,39
;607/97-99,101,102,109,108,103,104,139,140,148,152,105 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
WO 96/34568 |
|
Mar 1996 |
|
WO |
|
WO 99/08614 |
|
Dec 1998 |
|
WO |
|
Primary Examiner: Dvorak; Linda C. M.
Assistant Examiner: Ruddy; David M.
Attorney, Agent or Firm: Wilson, Sonsini Goodrich &
Rosati
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to U.S. application Ser. No.
60/123,440, filed Mar. 9, 1999, which is fully incorporated herein
by reference.
Claims
What is claimed is:
1. An apparatus for treating a tissue, comprising:
a handpiece assembly;
a dielectric electrode coupled to the handpiece assembly and
including at least one RE electrode with a front surface and a back
surface that is physically and electrically coupled to a back
surface of a dielectric, at least a portion of the dielectric
configured to contact a tissue surface; a cooling media delivery
member coupled to the dielectric electrode and configured to
deliver a cooling media to the back surface of the RF electrode;
and
a sensor coupled to the dielectric electrode.
2. The apparatus of claim 1, wherein the dielectric electrode is
configured to reduce at least one of an edge effect, an electrode
edge effect, an electrode temperature gradient an electrode current
density gradient or a tissue interface surface temperature
gradient.
3. The apparatus of claim 1 wherein the sensor is a thermal sensor,
a thermocouple, an optical sensor, a current sensor, voltage
sensor, an impedance sensor or a flow sensor.
4. The apparatus of claim 1, further comprising:
a source of cooling media coupled to the cooling media delively
member.
5. The apparatus of claim 4, wherein the cooling media is one of a
cooling fluid, a gas, a cryogenic gas, a liquid, an electrolytic
solution, a cooled liquid or a cryogenic liquid.
6. The apparatus of claim 1, wherein the handpiece includes at
least one of a connector, an electrical connector, a cooling media
connector, a lumen, a fluid lumen, a cooling media lumen; a flow
control device, a control valve or a nozzle.
7. The apparatus of claim 1, wherein the dielectric electrode
includes a tissue interface surface.
8. The apparatus of claim 7, wherein the tissue interface surface
has a shape configured to conform to an anatomical structure.
9. The apparatus of claim 8, wherein the tissue interface surface
has a curved shape.
10. The apparatus of claim 7, wherein the tissue interface surface
is conformable.
11. The apparatus of claim 10, wherein the tissue interface surface
is conformable to a skin surface.
12. The apparatus of claim 1, wherein the dielectric electrode has
a resistance that varies with a temperature.
13. The apparatus of claim 12, wherein the temperature is one of a
temperature of a tissue interface surface or a tissue positioned
adjacent to the tissue interface.
14. The apparatus of claim 1, further comprising:
a power source coupled to the dielectric electrode.
15. The apparatus of claim 14, further comprising:
feedback control resources coupled to at least one of the power
source, the dielectric electrode or the sensor.
16. The apparatus of claim 15, wherein the feedback control
resources include at least one of a microprocessor, a controller, a
software program set forth in a tangible media, a power control
circuit or a voltage and current monitor.
17. The apparatus of claim 1, wherein the RF electrode is a
monopolar electrode.
18. The apparatus of claim 17, further comprising:
an RE power supply electronically coupled to e RF electrode;
and
a ground pad electrode positioned on the skin and coupled to the RF
power source and the RF electrode.
19. The apparatus of claim 1, wherein the RF electrode is a bipolar
electrode and includes one of a plurality of electrodes, a
plurality of multiplexed electrodes, an array of electrodes or an
array of multiplexed electrodes.
20. The apparatus of claim 1, further comprising:
a switching device, wherein the RF electrode includes a plurality
of RF electrodes coupled to the switching device.
21. The apparatus of claim 20, wherein the switching device
includes one of a multiplexing device or a multiplexing device
configured to be coupled to an RF power source.
22. An apparatus for treating to skin, comprising:
a handpiece; and
a dielectric electrode coupled to the handpiece and including at
least One RF electrode with a front surface and a back surface that
is physically and electrically coupled to a back surface of a
dielectric, at least a portion of the dielectric configured to
contact a skin surface; and
a sensor coupled to the dielectric electrode.
23. The apparatus of claim 22, wherein the dielectric electrode is
configured to be capacitively coupled to the skin.
24. The apparatus of claim 22, wherein the RF electrode is a
monopolar electrode.
25. The apparatus of claim 22 further comprising:
an RF power supply electronically coupled to the RF electrode;
and
a ground pad electrode positioned on the skin and electronically
coupled to the RF power source and the R electrode.
26. The apparatus of claim 22, wherein the RF electrode is a
bipolar electrode and comprises one of a plurality of electrodes, a
plurality of multiplexed electrodes, an array of electrodes or an
array of multiplexed electrodes.
27. The apparatus of claim 26, further comprising:
a switching device coupled to at least a portion of the plurality
of RF electrodes, the switching device configured to be coupled to
at least one of a power supply or feedback control resources.
28. The apparatus of claim 27, wherein the switching device
includes one of a multiplexing device or a multiplexing device
coupled to an RF power source.
29. The apparatus of claim 22, wherein the dielectric electrode
comprises a plurality of dielectric portions including a first
portion and second portion.
30. The apparatus of claim 29, wherein the first and second
portions are substantially positioned on an energy delivery device
surface.
31. The apparatus of claim 30, wherein the first portion is
positioned within an interior area defined by the second
portion.
32. The apparatus of claim 31, further comprising:
a gap disposed between the first portion and the second
portion.
33. The apparatus of claim 31, wherein the first and second
portions have one of a substantially circular shape or an oval
shape.
34. The apparatus of claim 33, wherein the first and second
portions are substantially concentric.
35. The apparatus of claim 29, further comprising:
a switching device coupled to at least one of the plurality of
dielectric portions.
36. The apparatus of claim 35, wherein the switching device
includes one of a multiplexing device or a multiplexing device
coupled to an RF power source.
37. An apparatus for treating the skin, comprising:
a handpiece; and
an energy delivery device coupled to tie handpiece, the energy
delivery device having a conductive portion and a dielectric
portion, the energy delivery device configured to be coupled to a
power source, at least a portion of the dielectric portion
configured to contact a skin surface;
a cooling media delivery member coupled to the energy delivery
device; and
a sensor coupled to one of the energy delivery device, the energy
delivery device, the tissue interface surface or a power source
coupled to the energy delivery device.
38. The apparatus of claim 37, further comprising:
a pressure relief valve coupled to the energy delivery device.
39. The apparatus of claim 37, wherein the energy delivery device
is configured to reduce at least one of an edge effect, an
electrode edge effect, an electrode temperature gradient, an
electrode current density gradient or a tissue interface surface
temperature gradient.
40. The apparatus of claim 37, wherein the conductive portion is a
conductive layer and the dielectric portion is a dielectric
layer.
41. The apparatus of claim 40, wherein the conductive portion has a
surface area that is less than a dielectric layer surface area.
42. The apparatus of claim 40, wherein the energy delivery device
is configured such that substantially all of an energy delivery
device current flows through the conductive layer.
43. The apparatus of claim 40, wherein the dielectric layer is a
tissue contacting layer and the conductive layer is disposed on a
non-tissue contacting side of the dielectric layer.
44. The apparatus of claim 40, wherein the dielectric layer is one
of an oxide layer, a metal oxide layer, a polymer, a polyimide or a
diamond.
45. The apparatus of claim 40, wherein the dielectric layer has a
thickness of about 0.001 inches.
46. The apparatus of claim 40, wherein the conductive layer is one
of a metal, a metal alloy, copper or a conductive polymer.
47. The apparatus of claim 31, wherein the cooling media delivery
member delivers a cooling media to the energy delivery device and
cool at least a portion of the energy delivery device by at least
one of a conductive effect, an evaporative effect, a convective
effect or an ebullient cooling effect.
48. The apparatus of claim 37, further comprising:
a source of cooling media coupled to at cooling media delivery
member, the cooling media delivery member including at least one of
a flow control device and a control valve or a nozzle.
49. The apparatus of claim 48, wherein the cooling media is one of
a cooling fluid, a gas, a cryogenic gas, a liquid, an electrolytic
solution, a cooled liquid or a cryogenic liquid.
50. The apparatus of claim 37, wherein at least a portion of the
energy delivery device is flexible or elastic.
51. The apparatus of claim 50, wherein the energy delivery device
is one of a membrane, a flexible membrane, a skin conforming
membrane, a film, a flexible film or a skin conforming film.
52. The apparatus of claim 50, wherein the at least a portion of
the energy delivery device is deformable in response to a
pressure.
53. The apparatus of claim 52, further comprising:
a valve coupled to the handpiece, wherein the valve is one of a
control valve, a pressure valve or a pressure relief valve.
54. The apparatus of claim 53, further comprising:
feedback control resources coupled to at least one of the valve or
the sensor.
55. The apparatus of claim 37, wherein the conductive portion is an
RF electrode.
56. The apparatus of claim 55, wherein the RF electrode is a
monopolar electrode.
57. The apparatus of claim 56 further comprising,
an RF power supply electronically coupled to the RF electrode;
and
a ground pad electrode positioned on the skin and electronically
coupled to the RF power source and the RF electrode.
58. The apparatus of claim 55, wherein the RF electrode is a
bipolar electrode and comprises one of a plurality of electrodes, a
plurality of multiplexed electrodes, an array of electrodes or an
array of multiplexed electrodes.
59. The apparatus of claim 58, further comprising:
a switching device coupled to at least a portion of the plurality
of RF electrodes, the switching device configured to be coupled to
at least one of a power supply or feedback control resources.
60. The apparatus of claim 59, wherein the switching device
includes one of a multiplexing device or a multiplexing device
coupled to an RF power source.
Description
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus for
treating tissue. More particularly, the invention relates to a
method and apparatus for treating tissue using the controlled
delivery of energy.
DESCRIPTION OF RELATED ART
The human skin is composed of two elements: the epidermis and the
underlying dermis. The epidermis with the stratum corneum serves as
a biological barrier to the environment. In the basilar layer of
the epidermis, pigment-forming cells called melanocytes are
present. They are the main determinants of skin color.
The underlying dermis provides the main structural support of the
skin. It is composed mainly of an extracellular protein called
collagen. Collagen is produced by fibroblasts and synthesized as a
triple helix with three polypeptide chains that are connected with
heat labile and heat stable chemical bonds. When collagen
containing tissue is heated, alterations in the physical properties
of this protein matrix occur at a characteristic temperature. The
structural transition of collagen contraction occurs at a specific
"shrinkage" temperature. The shrinkage and remodeling of the
collagen matrix with heat is the basis for the technology.
Collagen crosslinks are either intramolecular (covalent or hydrogen
bond) or intermolecular (covalent or ionic bonds). The thermal
cleavage of intramolecular hydrogen crosslinks is a scalar process
that is created by the balance between cleavage events and
relaxation events (reforming of hydrogen bonds). No external force
is required for this process to occur. As a result, intermolecular
stress is created by the thermal cleavage of intramolecular
hydrogen bonds. Essentially, the contraction of the tertiary
structure of the molecule creates the initial intermolecular vector
of contraction.
Collagen fibrils in a matrix exhibit a variety of spatial
orientations. The matrix is lengthened if the sum of all vectors
acts to distract the fibril. Contraction of the matrix is
facilitated if the sum of all extrinsic vectors acts to shorten the
fibril. Thermal disruption of intramolecular hydrogen bonds and
mechanical cleavage of intermolecular crosslinks is also affected
by relaxation events that restore preexisting configurations.
However, a permanent change of molecular length will occur if
crosslinks are reformed after lengthening or contraction of the
collagen fibril. The continuous application of an external
mechanical force will increase the probability of crosslinks
forming after lengthening or contraction of the fibril.
Hydrogen bond cleavage is a quantum mechanical event that requires
a threshold of energy. The amount of (intramolecular) hydrogen bond
cleavage required corresponds to the combined ionic and covalent
intermolecular bond strengths within the collagen fibril. Until
this threshold is reached, little or no change in the quaternary
structure of the collagen fibril will occur. When the
intermolecular stress is adequate, cleavage of the ionic and
covalent bonds will occur. Typically, the intermolecular cleavage
of ionic and covalent bonds will occur with a ratcheting effect
from the realignment of polar and nonpolar regions in the
lengthened or contracted fibril.
Cleavage of collagen bonds also occurs at lower temperatures but at
a lower rate. Low level thermal cleavage is frequently associated
with relaxation phenomena in which bonds are reformed without a net
change in molecular length. An external force that mechanically
cleaves the fibril will reduce the probability of relaxation
phenomena and provides a means to lengthen or contract the collagen
matrix at lower temperatures while reducing the potential of
surface ablation.
Soft tissue remodeling is a biophysical phenomenon that occurs at
cellular and molecular levels. Molecular contraction or partial
denaturization of collagen involves the application of an energy
source, which destabilizes the longitudinal axis of the molecule by
cleaving the heat labile bonds of the triple helix. As a result,
stress is created to break the intermolecular bonds of the matrix.
This is essentially an immediate extracellular process, whereas
cellular contraction requires a lag period for the migration and
multiplication of fibroblasts into the wound as provided by the
wound healing sequence. In higher developed animal species, the
wound healing response to injury involves an initial inflammatory
process that subsequently leads to the deposition of scar
tissue.
The initial inflammatory response consists of the infiltration by
white blood cells or leukocytes that dispose of cellular debris.
Seventy-two hours later, proliferation of fibroblasts at the
injured site occurs. These cells differentiate into contractile
myofibroblasts, which are the source of cellular soft tissue
contraction. Following cellular contraction, collagen is laid down
as a static supporting matrix in the tightened soft tissue
structure. The deposition and subsequent remodeling of this nascent
scar matrix provides the means to alter the consistency and
geometry of soft tissue for aesthetic purposes.
In light of the preceding discussion, there are a number of
dermatological procedures that lend themselves to treatments which
deliver thermal energy to the skin and underlying tissue to cause a
contraction of collagen, and/or initiate a would healing response.
Such procedures include skin remodeling/resurfacing, wrinkle
removal, and treatment of the sebaceous glands, hair follicles
adipose tissue and spider veins. Currently available technologies
that deliver thermal energy to the skin and underlying tissue
include Radio Frequency (RF), optical (laser) and other forms of
electromagnetic energy. However, these technologies have a number
of technical limitations and clinical issues which limit the
effectiveness of the treatment and/or preclude treatment
altogether. These issues include the following: i) achieving a
uniform thermal effect across a large area of tissue, ii)
controlling the depth of the thermal effect to target selected
tissue and prevent unwanted thermal damage to both target and
nontarget tissue, iii) reducing adverse tissue effects such as
burns, redness blistering, iv) replacing the practice of delivery
energy/treatment in a patchwork fashion with a more continuous
delivery of treatment (e.g. by a sliding or painting motion), v)
improving access to difficult to reach areas of the skin surface
and vi) reducing procedure time and number of patient visit;
required to complete treatment, As will be discussed herein the
current invention provides an apparatus for solving these and other
limitations.
One of the key shortcomings of currently available RF technology
for treating the skin is the edge effect phenomena. In general,
when RF energy is being applied or delivered to tissue through an
electrode which is in contact with that tissue, the current
patterns concentrate around the edges of the electrode, sharp edges
in particular. This effect is generally known as the edge effect.
In the case of a circular disc electrode, the effect manifests as a
higher current density around the perimeter of that circular disc
and a relatively low current density in the center. For a square
shaped electrode there is a high current density around the entire
perimeter, and an even higher current density at the corners where
there is a sharp edge.
Edge effects cause problems in treating the skin for several
reasons. First they result in a nonuniform thermal effect over the
electrode surface. In various treatments of the skin, it is
important to have a uniform thermal effect over a relatively large
surface area, particularly for dermatologic treatments. Large in
this case being on the order of several square millimeters or even
a square centimeter. In electrosurgical applications for cutting
tissue, there typically is a point type applicator designed with
the goal of getting a hot spot at that point for cutting or even
coagulating tissue. However, this point design is undesirable for
creating a reasonably gentle thermal effect over a large surface
area. What is needed is an electrode design to deliver uniform
thermal energy to skin and underlying tissue without hot spots.
A uniform thermal effect is particularly important when cooling is
combined with heating in skin/tissue treatment procedure. As is
discussed below, a non-uniform thermal pattern makes cooling of the
skin difficult and hence the resulting treatment process as well.
When heating the skin with RF energy, the tissue at the electrode
surface tends to be warmest with a decrease in temperature moving
deeper into the tissue. One approach to overcome this thermal
gradient and create a thermal effect at a set distance away from
the electrode is to cool the layers of skin that are in contact
with the electrode. However, cooling of the skin is made difficult
if there is a non-uniform heating pattern. If the skin is
sufficiently cooled such that there are no burns at the corners of
a square or rectangular electrode, or at the perimeter of a
circular disc electrode, then there will probably be overcooling in
the center and there won't be any significant thermal effect (i.e.
tissue heating) under the center of the electrode. Contrarily, if
the cooling effect is decreased to the point where there is a good
thermal effect in the center of the electrode, then there probably
will not be sufficient cooling to protect tissue in contact with
the edges of the electrode. As a result of these limitations, in
the typical application of a standard electrode there is usually an
area of non-uniform treatment and/or burns on the skin surface. So
uniformity of the heating pattern is very important. It is
particularly important in applications treating skin where collagen
containing layers are heated to produce a collagen contraction
response for tightening of the skin. For this and related
applications, if the collagen contraction and resulting skin
tightening effect are non-uniform then a medically undesirable
result may occur.
SUMMARY OF THE INVENTION
One embodiment of an apparatus for treating the skin includes a
template having a tissue interface surface and an energy delivery
device coupled to the template. The energy delivery device is
configured to be coupled to a power source and has a variable
resistance portion. A sensor is coupled to one of the template, the
energy delivery device, the tissue interface surface or a power
source coupled to the energy delivery device.
In another embodiment the variable resistance portion is configured
to reduce an electrode edge effect.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a lateral view of embodiments of the skin treatment
apparatus illustrating components of the apparatus including the
treatment template, energy delivery device and tissue interface
surface.
FIG. 2a is a lateral view of an embodiment illustrating the use of
a handpiece coupled to the treatment template.
FIG. 2b is a lateral view of an embodiment illustrating the
delivery of cooling fluid to the electrode using lumens, nozzles
control valves and a control system. The figure also illustrates a
detachable electrode.
FIG. 3 is a lateral view of an embodiment illustrating the use of a
variable resistance coating on the surface of the electrode
FIGS. 4 and 5 are perspective and cross-sectional views
illustrating an embodiment of an electrode with rings of resistance
material interposed between conductive material to generate a
radial resistance gradient on the electrode surface.
FIGS. 6A and 6B are perspective and cross-sectional views
illustrating an embodiment of a cylindrical electrode with rings of
resistance material interposed between conductive material, the
resistance rings having increasing thickness moving in the outward
radial direction.
FIG. 7 is a cross-sectional/schematic view illustrating an
embodiment of a ringed electrode coupled to a switching device,
whereby duty cycle control of the conductive rings is used to
achieve a more uniform current density across the surface of the
electrode.
FIG. 8 is a cross-sectional/schematic view illustrating an
embodiment of an energy delivery device having a linear array of
bipolar electrodes.
FIG. 9 is a cross-sectional/lateral view illustrating an embodiment
of an electrode having a contoured thickness profile configured to
produce a resistance gradient across the surface of the electrode
to achieve a uniform current density.
FIG. 10a is a lateral view of an embodiment of an electrode
illustrating the use of a dielectric coating on the surface of the
electrode to achieve a uniform current density.
FIG. 10b is a perspective view of an embodiment of an electrode
illustrating the use of an attached and/or conformable dielectric
layer to achieve a uniform current density.
FIG. 11 is a schematic view illustrating the current path from the
dielectric-coated electrode to the body and return electrode for
monopolar electrode embodiments.
FIG. 12 is a schematic view illustrating the current through tissue
for dielectric -coated bipolar electrode embodiments.
FIG. 13 is a lateral view of an embodiment of a dielectric-coated
electrode where the dielectric coating comprises a copper coating
on a polyamide substrate.
FIG. 14 is a lateral view of an embodiment of a dielectric-coated
electrode where the dielectric coating comprises an oxide coating
grown on a conductive substrate.
FIG. 15 is a cross-sectional view of the skin illustrating the
target tissue zone and target tissue structures that can be treated
by embodiments of the invention.
FIG. 16 is a cross sectional/schematic view illustrating an
embodiment using a circulating cooled fluid to cool the
electrode.
FIG. 17a is a cross-sectional/schematic view illustrating an
embodiment using a coolant/refrigerant spray to cool an electrode
within an electrode housing.
FIG. 17b is a related embodiment to that shown in FIG. 17a where
the coolant spray is regulated by a solenoid valve coupled to an
electronic control system and/or a physician-activated foot
switch.
FIG. 18 is a flow chart for the selection of treatment parameters
such as cooling and heating sequences, durations etc.
FIG. 19 illustrates various embodiments of duty cycles cooling and
heating during different phases of treatment.
FIG. 20 is a cross-sectional view illustrating a bipolar electrode
embodiment comprising a dense array of multiple electrodes.
FIG. 21 depicts a block diagram of the feedback control system that
can be used with the pelvic treatment apparatus.
FIG. 22 depicts a block diagram of an analog amplifier, analog
multiplexer and microprocessor used with the feedback control
system of FIG. 21.
FIG. 23 depicts a block diagram of the operations performed in the
feedback control system depicted in FIG. 22.
DETAILED DESCRIPTION
The present invention provides an apparatus and methods for
overcoming the problems, limitations and clinical issues with
existing technology for treating the skin with radio frequency
(RF), optical (laser) and other forms of electromagnetic energy. In
various embodiments, the apparatus can be used to deliver thermal
energy to modify tissue including, collagen containing tissue, in
the epidermal, dermal and subcutaneous tissue layers including
adipose tissue. The modification of the tissue includes modifying a
physical feature of the tissue, a structure of the tissue or a
physical property of the tissue. The modification can be achieved
by delivering sufficient energy to cause collagen shrinkage, and/or
a wound healing response including the deposition of new or nascent
collagen. Various embodiments of the invention utilize novel
electrode designs and cooling methods for providing a more uniform
thermal effect in tissue at a selected depth while preventing or
minimizing thermal damage to the skin surface and other non target
tissue. The result is an improved aesthetic result/clinical outcome
with an elimination/reduction in adverse effects and healing
time.
In various embodiments the invention can be utilized for performing
a number of treatments of the skin and underlying tissue including:
dermal remodeling and tightening, wrinkle reduction, elastosis
reduction sebaceous gland removal/deactivation, hair follicle
removal, adipose tissue remodeling/removal and spider vein removal
and combinations thereof.
Referring now to FIGS. 1 and 2a, one embodiment of an apparatus 10
to treat the skin includes a treatment template 12. In various
embodiments, template 12 can be coupled to a handpiece 14. Also
template 12 can include a receiving opening 15 adapted to receive
and/or fit a body structure and make full or partial contact with
the skin layer of that structure. One or more energy delivery
devices 16 can be coupled to template 12 including receiving
opening 15, and can form an energy delivery surface 12' on template
12. Energy delivery devices can have a tissue contacting layer 16'
that delivers energy to the skin and/or underlying tissue. In
various embodiments, energy can be delivered to the skin and/or
underlying tissue, from energy delivery device 16, template energy
delivery surface 12' or a combination of both.
Energy delivery device 16 is coupled to an energy source 18.
Suitable energy sources 18 and energy delivery devices 16 that can
be employed in one or more embodiments of the invention include:
(i) a radio-frequency (RF) source coupled to an RF electrode, (ii)
a coherent source of light coupled to an optical fiber, (iii) an
incoherent light source coupled to an optical fiber, (iv) a heated
fluid coupled to a fluid delivery device, (v) a cooled fluid
coupled to a fluid delivery device, (vi) a cryogenic fluid, (vii) a
microwave source providing energy from 915 MHz to 2.45 GHz and
coupled to a microwave antenna, or (viii) an ultrasound power
source coupled to an ultrasound emitter, wherein the ultrasound
power source produces energy in the range of 300 KHZ to 3 GHz. For
ease of discussion for the remainder of this specification, the
energy source utilized is an RF source and energy delivery device
16 is one or more RF electrodes 16. However, all of the other
herein mentioned energy sources and energy delivery devices are
equally applicable to skin treatment apparatus 10.
A sensor 20 can be positioned at template energy delivery surface
12' or energy delivery device 16 to monitor temperature, impedance,
pressure and the like. Suitable sensors 20 include impedance,
pressure and thermal devices. Sensor 20 is used to control the
delivery of energy and reduce the chance of cell necrosis at the
surface of the skin as well as damage to underlying soft tissue
structures. Sensor 20 is of conventional design, and includes but
is not limited to thermistors, thermocouples, resistive wires, and
the like. A suitable thermal sensor 20 includes a T type
thermocouple with copper constantan, J type, E type, K type, fiber
optics, thermistors, resistive wires, thermocouple IR detectors,
and the like.
Referring now to FIG. 2b, in various embodiments handpiece 14 can
be configured for multiple functions and can include one or more of
the following: a fitting 14' for detachable electrodes, fluid and
gas fittings 14", electrical fittings 14'" (e.g. Lemo connectors)
for connection to power and control systems, a coolant valve 50 and
a coolant spray nozzle 52. Handpiece 14 could be configured to be
reusable, resterilized and compatible/interfacable with standard
medical and electronic connectors and fittings known in the
art.
Referring now to FIG. 3, one embodiment for achieving uniform
energy delivery from electrode 16 and minimizing edge effects
involves coating all or a portion of the electrode with a variable
resistance material 22 that has an electrical resistance that
varies with temperature. In one embodiment, variable resistance
material 22 is applied as a coating 22' on around tissue contact
surface 16'.
Variable resistance material 22 can be selected to have a positive
temperature coefficient of resistance (which means that its
resistance increases with temperature.). These materials known as
positive temperature coefficient semiconductors, can include
ceramic semiconductive materials and polymers with embedded
conductive particles. These and related materials, are well known
in the art and are used for thermostats and other solid state
temperature control devices. Such materials are available from the
Raychem Corporation (Menlo Park, Calif.), an established supplier
of positive temperature coefficient semiconductors. The use of such
a positive temperature coefficient coating 22' prevents and/or
reduces the formation of hot spots in the following manner. When
hot spots begin to form on the edges of a coated electrode due to
current concentration, the resistance of the coating 22' at the
electrode edges goes up, resulting in a reduction in current
flowing to and through these hot edges with an ultimate decrease in
temperature of the edges and tissue in contact or near the
edges.
Another embodiment for obtaining a more uniform energy delivery and
thermal effect in tissue is shown in FIGS. 4 and 5. In this
embodiment electrode 16, comprises a circular disc, with a number
of concentric conductive rings 24 of conductive material 24'.
Interposed between the conductive rings 24, are resistance rings 26
made of material with a higher electrical resistance, called
resistance material 26. The conductive and resistance rings 24 and
26 are configured such that there is a radial resistance gradient,
with a higher electrical resistance at the outer edges of the
electrode that decreases moving radially inwards. As a result, less
current flow (and hence less heating) occurs through the edges and
outer portions of the electrode compared to the more central
electrode portions. Another embodiment for achieving a radial
resistance gradient and minimizing hot spots, involves having
thicker rings of resistant material in the outer electrode portions
and progressively thinner resistance rings going toward the center
of the electrode. Varying the resistance of the energy delivery
surface 16' of the electrode, through the use of interposing rings
of conductive and resistance material serves to increase the
uniformity of current density across the electrode energy delivery
surface 16', resulting in a more uniform delivery of energy to
underlying tissue.
In related embodiments shown in FIGS. 6A and 6B, electrode 16 is
cylindrically shaped and is fabricated such that it is made out of
alternating layers of resistance material 26' and conductive
material 24'. The bottom portion of the electrode is the tissue
contacting surface 16' and hag s pattern of annular rings
correlating to the layers of resistance and conductive material.
Specifically, cylindrical electrode 16 is constructed such that the
resistance rings 26 near the electrode center 16" are thinner than
those at the outer edges 16'" with a continuous increase in
thickness moving in the outer radial direction. As result of this
configuration, electrons flowing through electrode outer electrode
edges 16'" must flow through more of resistance material 26 (e.g.
encounter more resistance) than those flowing through the more
central electrode portions 16". Consequently, the net current flow
on outer edges 16'"is less than in the more central electrode
portion 16". This ringed pattern can be made to a mathematical
limit where the annular rings become thinner and thinner and closer
and closer to one another such that there is almost a continuous
tissue contacting surface of conducting material 24, but also with
a continuous resistance element that causes the current flow to be
less on the outer electrode edges 16'" than the inner portions
16".
Referring now to FIG. 7, a related, but different, embodiment for
reducing edges effects also involves dividing a circular disc
electrode into annular conductive rings. However in this case, the
flow of current through the rings is temporally controlled using a
time sharing or duty cycle approach to turn on current flow to the
inner and outer rings for fixed time periods. During a given duty
cycle, RF current flow to the outer rings is turned on for the
shortest periods of time with progressively longer on- times time
moving inward in the radial direction. Although when the outer
rings are turned on, they briefly have a higher current flow and
are transiently hotter, this is compensated for by having them on
for only a short time period and/or shorter than more centrally
located electrode rings. Over time (e.g. on a time average basis)
the result is a more uniform energy delivery to the tissue and
hence thermal effect over the surface of the electrode. Adjacent
rings can be switched on and off sequentially or in any other
predetermined order or pattern. Also two or more rings can be
turned on at the same time. The switching of rings can be
controlled by a switching device/circuit 28, known in the art,
electrically coupled to the rings. Also, the rings can be
multiplexed to energy source 18 using a multiplexing circuit 30
known in the art.
In another embodiment shown in FIG. 8, the energy delivery device
16 can comprise a number of small rectangular shaped electrodes
that are laid down (on a supporting surface, structure or
substrate) and operated in a bi-polar fashion. In this embodiment,
every pair of bars could be a bi-polar electrode pair 17 possibly
with sequential switching between different pairs of bars to create
a bi-polar effect.
In still other alternative embodiments for controlling electrode
resistance and providing uniform energy delivery, electrode 16 can
be fabricated such that it has a continuous variation in resistance
moving in a radial or other direction. More specifically, the
electrode can be configured to have a continuously decreasing
resistance moving inwardly in the radial direction. One embodiment
for achieving this result is shown in FIG. 9, which illustrates an
electrode fabricated to have a tapered or otherwise contoured
profile, thickest at the outer edges 16'" and thinner moving inward
in the radial direction. By definition, the thicker sections of the
electrode have increased resistance compared to the thinner
sections (e.g. resistance is proportional to thickness). In a
related, but distinct embodiment, a radial or other directional
gradient in resistance can be achieved by doping, impregnating or
coating the surface of the electrode with materials (known in the
art) to increase its electrical resistance.
Referring to FIGS. 10a and 10b, other embodiments of the invention
for achieving a more uniform thermal effect, involve the use of a
layer of dielectric material coupled to the electrode and
positioned between the conductive portions of the electrode and the
skin. In one embodiment shown in FIG. 10a, all or a portion of
electrode 16 can be coated with a dielectric material 32 to form a
dielectric layer 32'. In a related embodiment shown in FIG. 10b,
electrode 16 is attached to a dielectric layer or film 32', which
can be made of a conformable material that conforms to the surface
of the skin. In various embodiments, the electrode 16 that is
attached to dielectric layer 32' can be of any geometry, e.g.
circular, oval, rectangular, etc. It is desirable to have the
surface of the dielectric layer 32' extend beyond the edges of
electrode 16 such that substantially all current must flow through
the dielectric layer. This can be achieved by configuring electrode
16 to have a smaller surface area than layer 32' and having
electrode 16 substantially centered on the surface of layer 32'.
Accordingly, electrode 16 can have between 1 to 100% the surface
area of layer 32', with specific embodiments 25, 50, 75%, and
90%.
There are several key benefits to the use of dielectric layer 32'
with electrode 16, the most important of which is the ability to
produce a more uniform current flow through the electrode and
subsequently to the underlying skin and tissue. This is
attributable in part to a capacitance effect created by the use of
layer/coating 32'. Specifically, the use of layer 32' creates an
electronic capacitor (e.g., two conductors separated by an
insulator) where, one conductor is the electrode, the second
conductor is the skin or the tissue being treated, and the
insulator separating them is the dielectric layer on the electrode.
In various embodiments, the capacitive effect of dielectric layer
32 can be controlled through the selection of the thickness,
surface area and dielectric constant of layer 32, as well as by
controlling the frequency of the RF signal.
As a result of the above configuration, the dielectric coating
creates an increased impedance to the flow of electrical current
through the electrode. Owing to this increased impedance, and to
the fact that electrical current naturally seeks the path of least
impedance, the current is biased/forced to take the shortest path
length between the two conductors, which is the path straight down
through the electrode to the tissue. By corollary, the electrical
current is unlikely to take any paths that would result in a longer
path length and hence increased impedance. Such a longer path
length would be the case for any concentration of current flowing
out of the edges of the electrode.
The use of the dielectric coating serves to force a more uniform
distribution of electrical current paths across the electrode
surface and down into the tissue. This occurs because the
capacitance resulting from the dielectric coating presents
impedance to the flow of electrical energy particularly at the
edges of the electrode, where current concentrations are likely to
occur. More specifically, the use of dielectric coating 32'
produces a more uniform impedance through the electrode and causes
a more uniform current to flow through the electrode. The resulting
effect minimizes or even eliminates, edge effects around the edges
16'" of electrode 16 which includes the perimeter for a circular
disk-shaped electrode, and the perimeter and corners for a
rectangular electrode. It is desirable to have the electrical
impedance of the dielectric layer 32' to be higher than that of the
tissue. In various embodiments, the impedance of layer 32' at the
operating frequency, can be in the range of 200 .OMEGA. per square
centimeter or greater. Suitable materials for a dielectric coating
32' include, but are not limited to, Teflon.RTM. and the like,
silicon nitride, polysilanes, polysilazanes, polyimides, Kapton and
other polymers, antenna dielectrics and other dielectric materials
well known in the art.
Another advantage of using a dielectric layer 32' is that there is
little or no increase in current density resulting from only
partial contact of electrode 16 with the tissue surface. Normally,
such partial contact would increase current density in the
electrode portions remaining in contact with tissue increasing the
size and severity of hot spots and the likelihood of spark
discharge and burns to the tissue. However, because of the
capacitance effect of the dielectric layer, the impedance of the
electrode goes up (due to a decrease in the capacitance) as the
surface area of the electrode tissue contact zone is reduced. This
causes the current density flowing through the electrode to remain
relatively constant. This effect is achieved by configuring the
dielectric layer/electrode to have an impedance higher than the
contacting tissue.
Hence, use of the dielectric coating on the electrode presents an
important safety advantage over the use of just a conductive
electrode in contact with the tissue, since there is little or no
increase in current density and resulting hot spots from only
partial tissue contact of the electrode.
Such partial contact with a conventional electrode, not only cause
the edge effects and hot spots, but as the amount of tissue contact
decreases, the current density can increase to the point where the
electrode begins to act like a electrosurgical knife (e.g. a bovie)
with a spark discharge causing serious burns to the patient and
also possibly to the medical practitioner. In contrast for the
dielectric-coated electrode, partial tissue contact at a point
would result in almost no current flowing because the impedance
would be very high. Thus, embodiments using the dielectric- coated
electrode have safety advantages in the clinical setting where
partial tissue contact often occurs.
Another advantage of the use of a dielectric coating is the
minimization of the need to use a conductive fluid (e.g. saline
solution) to conduct RF energy to the skin surface and/or assure
electrical contact of the electrode with the skin surface. The use
of conductive fluids minimizes tissue contact problems when the
electrode is a conductive electrode. However for embodiments using
a dielectric coating electrode, the conductive fluid is less
important because the dielectric coating causes capacitively
coupling of the energy into the tissue. This is a distinct
advantage from several standpoints. First is from an ease of use
standpoint, since fluids and/or conductive gels can be difficult to
work with. The second advantage is one of safety and control, since
the physician can not always control where the fluid goes, possibly
heating and burnring tissue not intended to be treated, as well as
presenting a possible shock hazard to the patient and medical
personnel. The third advantage is reproducibility, since conductive
fluids having different electrolyte concentrations will have
different conductivities and hence, cause more or less current to
be conducted to the tissue causing varying amounts of heating.
In various embodiments, a dielectric-coated electrode can be
bi-polar or mono-polar. For a mono-polar configuration (shown in
FIG. 11), electrode 16 can comprise a single electrode covered with
a dielectric coating 32' that capacitively couples energy into the
skin or other tissue used in conjunction with a return electrode
34. While for bi-polar embodiments, a capacitively coupled
electrode can comprise multiple electrodes delivering energy to the
skin. Referring now to FIG. 12, in one bi-polar embodiment (with
the dielectric coating on the tissue contacting side), electrical
current uniformly flows out from a first electrode 17' of a
bi-polar pair 17 through its dielectric coating into the tissue
then through the dielectric coating of the second electrode 17" of
the bi-polar pair 17 into the second electrode and then back to the
RF energy source 18. The area of substantial current flow and hence
the treatment zone 44 is substantially confined to an area of
tissue between each bipolar pair 17 of electrodes. Because of the
benefits of dielectric coating described herein, the current
flowing through this area is very uniform resulting in a uniform
thermal effect as well.
Referring now to FIG. 13, another embodiment of a dielectric
coated/capacitively coupled electrode can comprise a copper coating
36 adhered to a polyimide substrate 38 that is about 0.001" in
thickness. Such an electrode is similar to a standard flex circuit
board material commercially available in the electronics industry;
however in this case the flex circuit substrate (e.g. the polyamide
layer) is much thinner than that found in a standard electric
circuit board. The copper-polyimide laminate material can be an
off-the-shelf commercially available material and the deposition of
copper down on polyimide is a well-known process in the circuit
board industry. However, the present invention uses this material
in a fashion contrary to its standard or known usage or
configuration. Specifically rather than having the copper in
contact with the intended electrical device/circuit (e.g. the skin)
as a conductive electrode, the polyimide is touching the skin and
the copper is separated from the skin with the 0.001" (1 mil)
polyimide layer. At standard electrosurgical operating electrical
frequencies (e.g. several hundred KHz to perhaps a MHz), the 1 mil
layer of polyimide is too thick and does not perform well as a
capacitor from an electrical standpoint. One way of improving the
performance of a 1 mil polyimide copper electrode is to increase
the frequency of the RF current going to the copper-polyimide
electrode. In various embodiments using 1 mill polyimide-copper
electrodes, the RF current supplied to the electrode can be
operated at approximately six MHz. In embodiments with a thinner
polyimide layer (e.g. less than 0.001), the frequency of the RF
current can be reduced to the standard range recited above. One
method for decreasing the thickness of the polyimide layer would be
to grow the copper layer on the polyimide using sputtering,
electrodeposition, chemical vapor deposition, plasma deposition and
other deposition techniques known in the art. These methods could
be equally applicable to other thin polymer dielectric films known
in the art. Alternatively these same processes could be used to
deposit a dielectric layer such as paralyne, onto a conductive
layer. Also, the copper layer could be adhered to a thinner 0.0003"
polyimide film.
Referring now to FIG. 14, yet another embodiment of a
dielectric-coated electrode involves growing an oxide layer
(usually a metal oxide layer) 40, on a conductive material 42 such
as a metal conductor. The use of oxide layer 40 presents a number
of possible technical advantages. The first of which is a reduced
thermal resistance and hence improved heat transfer through
electrode 16 and ultimately through the skin verses metal-polymer
film and other electrodes. specifically the thermal conductivity of
a deposited oxide film (such as an aluminum oxide on an aluminum
conductive layer) is significantly improved over that of a
polyimide layer. This improves thermal conductivity, in turn
improving the ability to cool and protect the skin by improving the
transfer of heat from skin through the electrode, enabling the
electrode to better dissipate heat from the skin (by convection and
conduction) both with and without cooling of the electrode
conduction. The net effect is to improve the cooling efficiency of
the skin. For example, an aluminum oxide layer grown on an aluminum
conductor has a thermal conductivity approximately 20 to 100 times
better than a polyimide layer. Aluminum oxide layers can be readily
grown on an aluminum using the commercially available process of
anodization. The result is an electrode that has a dielectric layer
32', the aluminum oxide, which is also a very good thermoconductor.
Oxide layers can also be grown on titanium, platinum, stainless
steel, silver, gold and other conductors using similar anodization
or other commercially available processes known in the art.
Thus, the use of dielectric-coated electrodes or otherwise
capacitively coupled electrodes has one or more of the following
advantages: i) improved the ability to uniformly treat tissue (e.g.
more uniform thermal effect), ii) improved safety features such as
partial tissue contact not resulting in burns, and minimizes the
requirement for an electrically conducting fluid or electrolytic
fluid to couple the electrode into the tissue; and iii) improved
cooling ability for oxide coated electrodes such as an aluminum
oxide coated aluminum electrode.
Referring now to FIG. 15, the target tissue zone 44 for therapy
(also called therapeutic zone 44, or thermal effect zone 44), can
include, but is not limited to, tissue at a depth from
approximately 100 .mu.m beneath the surface of the skin down to as
deep as a couple of millimeters, depending upon the type of
treatment (e.g. collagen contraction, hair removal, etc.). For
treatments involving collagen contraction, it is desirable to cool
both the epidermis and the superficial layers of the dermis of the
skin which lies beneath the epidermis, to a cooled depth range
between 100 m to several hundred m.
In various embodiments, the invention can be used to treat
different structures 44' of the skin lying at different depths.
Such structures can include the hair follicles and sebaceous glands
and related structures. The invention can even be used to treat
deeper structures or tissue such as the subcutaneous fat layer.
Treatment in this case meaning the delivery of thermal or other
energy to that tissue to produce a therapeutic effect. As such
cooling may be important in each of these applications.
Turning now to a discussion of optimal control of the cooling
process, all the devices disclosed in this application can
incorporate some form of a cooling device 46, system 46' and/or
method (see FIGS. 16 and 17). Cooling device 46 or system 46' can
be configured to precool the surface layers of the target tissue
such that when the electrode structure is in contact with the
tissue and/or prior to turning on the RF energy source the
superficial layers of the target tissue are already cooled. When RF
energy source is turned on or delivery of RF to the tissue
otherwise begins, resulting in heating of the tissues, the tissue
that's been cooled is protected from thermal effects including
thermal damage. The tissue that has not been cooled will warm up to
therapeutic temperatures resulting in the desired therapeutic
effect.
In various embodiments, the treatment process can include one or
more of the following steps: i) precooling (before the delivery of
energy to the tissue has started), ii) an on phase or energy
delivery phase in conjunction with cooling, and iii) post cooling
after the delivery of energy to tissue has stopped. Pre-cooling
gives time for the thermal effects of cooling to propagate down
into the tissue. More specifically, precooling allows the
achievement of a desired tissue depth thermal profile, with a
minimum desired temperature being achieved at a selectable depth.
This can be facilitated with the use of thermal sensors positioned
within or on the skin. The amount or duration of precooling can be
used to select the depth of the protected zone of untreated tissue.
Longer durations of precooling produce a deeper protected zone and
hence a deeper level in tissue for the start of the treatment zone.
The opposite is true for shorter periods of precooling, all other
factors (e.g. RF power level) being relatively equal.
Post cooling can be important because it prevents and/or reduces
heat delivered to the deeper layers from propagating upward (via
conduction) and warming up the more superficial layers possibly to
therapeutic temperature range even though external energy delivery
to the tissue has ceased. In order to prevent this and related
thermal phenomena, it is desirable to maintain cooling of the
treatment surface for some period of time after application of the
RF energy has ceased. In various embodiments varying amounts of
post cooling can be combined with "real time cooling" and/or
precooling.
Various embodiments of the invention may employ different cooling
methods and those cooling methods can be configured for the
specific treatment method or structure being treated (e.g.
treatment of the sebaceous glands). Referring now to FIG. 16, one
embodiment of cooling involves the circulation of a coolant or cold
fluid 48, inside a hollow dielectric-coated electrode or other
electrode structure such that this cooling fluid is an intimate
contact with the electrode. As a result, when the electrode is in
contact or close proximity to the skin, this cooling fluid also
cools the skin via thermal conduction and/or radiation of heat from
the skin to the electrode and then the transfer of heat from the
electrode to the cooling solution by convection and conduction. In
these and related embodiments it is beneficial to have good heat
transfer through the cooling fluid, the electrode and the tissue to
be cooled. Optimization of heat transfer through the electrode can
be facilitated by the selection of materials (e.g. materials with
high thermal conductivity such as metals), dimensions (e.g.
thickness, etc.) and shape. Accordingly, heat transfer through the
copper-polyamide electrode and related electrode embodiments can be
optimized by minimizing the thickness of the polyamide layer. This
will allow these types of electrodes to have good thermal coupling
to the tissue. For the case of the metal oxide- metal electrodes
(such as the aluminum-aluminum oxide electrode), metal oxide
dielectric layer 40 has a much higher thermoconductivity than the
polyamide dialectic, allowing a thicker dielectric layer and a
thicker electrode. These factors allow for stronger electrode
structure and potentially a higher degree of electrode capacitance
and capacitive coupling.
Referring now to FIG. 17a, other embodiments of the invention
utilizing cooling can incorporate a spray valve 50 (or valve 50)
coupled to a nozzle 52 positioned inside in the 54'0 interior of a
hollow electrode structure/housing 54 of electrode 16. Nozzle 52 is
used to spray a coolant or refrigerant 48 onto the inner surface
54" of the electrode structure 54, where it evaporates and cools
the electrode. Refrigerant 48 cools the electrode 16 by combination
of one or more of evaporative cooling, convection and conduction.
The electrode in turn, cools the tissue that is beneath it through
conduction. Possible refrigerants 48 include, but are not limited
to, halogenated hydrocarbons, carbon dioxide and others known in
the art. In a specific embodiment, the refrigerant is R134A which
is available from Refron, Inc. (38-18 33rd St. Long Island City,
N.Y. 11101) and commonly used to cool electronic components.
There are several advantages to cooling using an evaporating
refrigerant (also known as a cryogen). First, this type of cooling
known as evaporative cooling allows more precise temporal control
of the cooling process. This is because cooling only occurs when
the refrigerant is sprayed and it is evaporating (the latter being
a very fast short lived event). Thus cooling ceases rapidly after
the spray of refrigerant is stopped. The overall effect is to
confer very precise time on-off control of the spray. Improved
temporal control can also be obtained through the use of thin
electrodes having negligible thermal mass, alone or in conjunction
with a refrigerant spray. The negligible thermal mass of such
electrodes results in an almost instantaneous cooling of the
electrode and underlying skin.
In another embodiment shown in FIG. 17b, spray valve 50 can be a
solenoid valve 50, which can be fluidically coupled to a cryogen
reservoir 48'. Solenoid valve 50 can be electronically coupled to
and controlled by an electronic/computer control system 56 or
manually controlled by the physician by means of a foot switch 53
or similar device. Such valves have response times on the order of
five to ten milliseconds. Suitable solenoid valves include, but are
not limited to a solenoid pinch valve manufactured by the
N-Research Corporation (West Caldwell, N.J.).
In various embodiments, the electrode can have a variety of hollow
structures which are simultaneously configured for spray cooling of
the electrode and conductive cooling of the skin in contact with
the electrode. This can be accomplished by a combination of one or
more of the following i) maximizing the internal hollow surface
area of the electrode, minimizing the wall thickness of the
electrode in contact with the skin, and iii) designing the hollow
area of the electrode to maximize the internal surface area that
can be reached by the spray jet of a nozzle. It is also desirable
to have an opening in the electrode, or chamber containing the
electrode, to allow the evaporated refrigerant to escape. This
escape can include a pressure relief valve to control pressure in
the chamber.
In other embodiments involving use of refrigerants, cryogen 48 can
be dispersed or sprayed through a porous or open cell structure
(which can include the electrode) that can be configured to have
cryogen 48 make direct contact with the skin if necessary. In
another embodiment, the refrigerant is sprayed on the inside of a
hollow electrode tubular structure, with the electrode external
surface in contact with the skin. It is beneficial in this design
to make the electrode surface strong enough (e.g. able to withstand
compressive forces greater than 0.1 to 1 lbs) so that the electrode
can support itself when pressed against the skin in order to
improve heat transfer between the skin and the electrode. This can
be accomplished through the selection of higher strength electrode
materials, electrode thickness and shape. One embodiment of a
structurally strong electrode involves the use of a metal oxide
electrode such as titanium oxide electrode.
In alternative embodiments, portions of electrode 16 can be
configured to be sufficiently flexible to conform to the skin, but
still have sufficient strength and/or structure to provide good
thermal coupling when pressed against the skin surface. Such a
configuration can be utilized with a polyamide (or other polymer)
copper film electrode that needs to be kept thin to optimize
thermal conductivity. In these and related embodiments, the
electrode may comprise or be integral to a hollow tissue probe that
has a tissue contacting electrode external surface and an internal
electrode surface that is integral to or otherwise exposed within
an internal chamber of the probe where evaporation of the
refrigerant takes place. The internal chamber of the hollow
electrode 54 or probe is sealed, but can include a venting means
58.
In one embodiment shown in FIG. 17b, venting means 58 can be a
pressure relief valve 58 vented to the atmosphere or a vent line.
When the refrigerant spray comes into contact with the electrode
and evaporates, the resulting gas pressurizes the inside of this
sealed chamber/cylinder causing the thin flexible tissue contacting
electrode surface to partially inflate and bow out from the surface
of the supporting structure of the tissue probe. This
inflated/pressurized configuration provides the thinner
polyamide-copper film electrodes with a tissue contacting
surface/structure with sufficient strength to provide good thermal
coupling when pressed against the skin, while when in a deflated
state or if there is no pressure in the chamber, the electrode
remains flexible. In these and related embodiments, the refrigerant
spray serves two purposes. First, to cool the electrode and the
tissue adjacent the electrode, and second, to inflate/expand at
least portions of the electrode and/or chamber carrying the
electrode in order to provide an electrode/chamber structure
configured for good thermal coupling to the skin. In various
embodiments, the inflated electrode configuration can be configured
to enhance thermal contact with the skin and also result in some
degree of conformance of the electrode surface with the skin.
In various embodiments, relief valve 58 can be configured to open
at pressures including but not limited to 0.1 psi to 30 psi, with a
preferred narrower range of 0.5 to 5 psi and specific embodiments
of and 0.5, 1, 2, 4, 8, 14.7, 20 and 25 psi. Also in various
embodiments, the probe chamber can be fabricated from stainless
steel and other machinable metals known in the art. Suitable
pressure relief valves 58 include, but are not limited to,
mechanical valves including spring actuated valves, polymer valves,
and electronically controlled valves. In one embodiment pressure
relief valve 58 can be of a mechanical type manufactured by the
McMaster-Carr Corporation. The spring-actuated valves arc
controlled by an internal spring opens the valve, when the pressure
reaches a certain level. Embodiments using the electrically
operated valves, can include a pressure sensor/transducer 20
positioned inside the chamber and an electronic controller 56 which
is electronically coupled to both the electronic valve and the
pressure sensor. The controller sends a signal to open the valve
when a programmed pressure has been reached.
In various embodiments, cryogen spray 48 is used as cooling source
through evaporative cooling and contact with the electrode that's
touching the skin, and also to inflate a probe/electrode chamber to
provide pressure which will inflate and/or bow out the thin
flexible electrode to provide improved contact (e.g. thermal and
mechanical) with the skin and also some degree of conformance with
the skin. In embodiments employing higher chamber pressures,
approximately 10 to 20 psi, the flexible thin polyamide electrode
tissue contacting structure can become very rigid, and can have
similar properties (e.g. stiffness, rigidity etc.) to Mylar.RTM..
Then, decreasing the pressure several psi (e.g. 1 to 4 psi) the
rigidity decreases and the tissue contacting surface of the
electrode begins to become conformable. Thus, the rigidity and/or
conformity of the electrode can be selectable with chamber pressure
and adjusted for the mechanical properties and shape of the skin
surface being treated in order to obtain the desired level of
thermal coupling to the skin. Chamber pressures between five to ten
psi have been found to perform well for many applications. More
rigid structures can be obtained at higher chamber pressures, and
contrarily very flexible conformable structures can be obtained at
lower pressures. In alternative embodiments, the use of a sealed
evaporation chamber and "bowable" electrode could also be employed
with electrodes having a dielectric oxide layer, such as the
aluminum-aluminum oxide. In such embodiments, electrode thickness,
surface length and support structure are configured to allow the
electrode surface to bow outward with pressure in the 1 to 10 psi
or other range disclosed herein. The flexibility of a metal
electrode can be increased using one or more of the following
approaches: by making the electrode thinner, increasing the
unsupported length of the electrode surface and using
materials/processing methods with reduced stiffness (e.g. Young's
Modulus). In one embodiment an aluminum-aluminum oxide electrode
could be in the form of a foil type electrode and may have a
comparable thicknesses to commercially available aluminum foil.
Improved thermal response time is another advantage of embodiments
using sprayed cryogen 48 for cooling purposes. Circulating water
cooling systems have the limitation of not being able to have fast
enough thermal response times due to a number of factors (e.g.
thermodynamic properties of water, heat and mass transfer
limitations, etc.). The use of the spray cryogens in combination
with a thin film electrode (e.g. polyamide-copper) overcomes these
limitations and provide& the capability to perform a number Of
different types of algorithms for skin treatment that could not be
performed with a circulating cold water cooling system. For
example, the refrigerant spray could be turned on the order of
milliseconds before the start of RF energy delivery to the desired
tissue and subsequently cycled off and on in millisecond durations.
In various embodiments this could be accomplished using
commercially available solenoid valves coupled to a cryogen supply
(e.g. a compressed gag canister) or the cryogen delivery loop. Such
valves have response times on the order of five to ten
milliseconds. In various embodiments, these valves could be coupled
to a computer control system or could be manually controlled by the
physician by means of a foot switch or similar device. One of the
key advantages of this and related systems is the ability to
rapidly respond and cool overheated tissue before the occurrence of
thermal injury.
In alternative embodiment; the cryogen nozzle and solenoid valve
can be coupled to or otherwise configured to be used with a chopper
wheel (not shown). The chopper wheel is adapted for intermittently
allowing the spray of the cryogen onto the tissue or electrode.
This configuration provides the ability to shorten both the
response time and the duration of cooling. In these and related
embodiments, the cryogen spray is directed at an approximate
perpendicular angle into the face of a chopper wheel that rotates
at selectable angular velocity. The chopper wheel has an
approximately circular geometry and has an open section, which can
be a sector, radially oriented rectangle, or other geometric shape
positioned at a selectable position on the face of the wheel. When
the open section is aligned with refrigerant spray stream coming
out of the solenoid valve then the spray goes down and hits the
tissue. In various embodiments, the chopper wheel can rotate at
angular velocities between 1 and 10,000 rpm. The wheel, wheel
mechanism and timing system can be similar to those used on optical
chopper wheels well known in the art. Alternatively, various high
speed small motor mechanisms (such as a brushless dc motor) can
also be used.
An important advantage of embodiments of the invention employing a
solenoid valve alone, or in combination with a chopper wheel is the
ability to deliver the cryogen in very short bursts (via spray or
other means). This short burst capability allows the physician to
titrate and/or selectively control the amount of heat removed by
the cryogen from the tissue. This is because from a thermodynamic
standpoint, the amount of heat removed by a given volume of a given
cryogen as it evaporates is predictable (e.g. known latent heat of
vaporization, known cryogen temperature, etc.) So for a milliliter
volume of cryogen spray, the number of calories of heat loss from
the tissue can be predicted with a reasonable degree of accuracy
(e.g.. approx +/-5% or better). This information can be used to
design a treatment algorithm that's very quantitative, e.g. the
amount of cooling delivered is correlated to the RF power level or
other metric of energy delivery. Moreover, the algorithm can be
configured to control the amount of thermal energy (e.g. heating)
delivered to the tissue in an accurate manner in order to obtain a
desired tissue temperature and/or effect at selectable depth and
similarly can control the amount of cryogen delivered to the tissue
to produce a selectable amount of cooling sufficient to protect non
target tissue from thermal injury. Such ratios of cooling delivered
to energy delivered can be preprogrammed into the algorithm and can
be configured for depth of tissue to be treated, type of tissue
(e.g. skin vs. adipose tissue), thermal conductivity of treated
skin or tissue, desired target tissue temperature and desired
maximum non target tissue temperature. For example, when delivering
RF power at a 100 watt level for 0.1 second (assuming that 50% of
this heat propagates upward to a non target skin/tissue site), the
volume of cryogen delivered would have to be able to cool/remove 5
joules of energy from the tissue. If each ml of cryogen spray
removed one joule of energy by evaporation, then 5 ml of cryogen
would have to be delivered to the tissue. This could be delivered
in the same 0.1 seconds as the energy delivery or could be
delivered in series of ten 0.010 second burst over 0.2 seconds with
0.2 ml of cryogen per spray burst.
A key advantage of the cryogen spray is the availability to
implement rapid on and off control, with the 0.005 second response
times for solenoid valves, or even faster with embodiments using
some type of electronically controlled aperture or shutter known in
the art. In various embodiments, a varied number of pulse on-off
type cooling sequences and algorithms may be employed. In one
embodiment, the treatment algorithm comprises precooling the tissue
by starting a cryogen spray, followed by a short pulse of RF energy
into the tissue, with the cryogen spray continuing during the
duration of the energy delivery and then stopping shortly
thereafter (e.g. on the order of milliseconds). This or another
treatment sequence could be repeated again. Thus in various
embodiments, the treatment sequence can comprise a pulsed sequence
of cooling on, heat, cooling off, cooling on, heat, cool off, and
with cooling and heating durations on orders of tens of
milliseconds. In these embodiments, every time the surface of the
tissue of the skin is cooled, heat is removed from the skin
surface. However this cooling effect is not appreciable for the
deeper tissue away from the surface area where the cryogen spray is
directed and having its effect. In various embodiments, the cryogen
burst duration and interval between burst can be in the tens of
milliseconds ranges which allows surface cooling, while still
delivering the desire thermal effect into the deeper target
tissue.
In various embodiments, the burst duration and interval can be
adjusted for the heat transfer rate/thermoconductivity between
deeper target tissue and the skin such that the cooling rate of the
skin equal or exceeds the rate of heat transfer from the RF heated
deeper target tissue to the skin. The rapid response time and
precise temporal control of embodiments of the invention employing
burst cryogen spray cooling allows the performance of a number of
noninvasive tissue treatment methods that could not be performed by
apparatus/methods employing water and other slower, less
controllable cooling methods due to a risk of thermal injury of
nontarget tissue and other thermal related complications. Such
noninvasive treatment methods include skin resurfacing, collagen
shrinkage, treatment of sebaceous glands, hair follicle removal,
treatment/removal of subcutaneous fat and other skin treatments
known in the art of dermatology or plastic surgery.
In various embodiments, the depth of the thermally effected zone
(also called the thermal effect zone) can be controlled by the
amount of precooling. Specifically, the longer periods of
precooling (for a given rate of energy delivery, or total amount of
energy delivered), result in a deeper penetration in the tissue
before the thermal effect starts. In contrast, little or no
precooling results in the thermal effect starting at or near the
skin surface. In related embodiments, the thickness of the thermal
effect zone in the tissue can be controlled by the duration of the
RF energy delivery. The longer the period of RF energy delivery,
the deeper the thermal effect.
In still other related embodiments, the starting depth and
thickness of the thermal effect zone can be selected through
control of both the duration/amount of precooling and the duration
of RF energy delivery. Such control presents a distinct advantage
in that it allows the selected treatment of a discrete anatomical
layer or tissue structure located at various depths within or
beneath the skin without injury to surrounding tissue. This and
other benefits can be derived from the combination of cryogen spray
with pulsed cooling and/or heating.
Different treatment algorithms can incorporate different amounts of
precooling, heating and post cooling phases in order to produce a
desired tissue effect at a desired depth. FIG. 18 is a flow chart
for the selection of treatment parameters including, duration of
precooling, RF on time, RF power levels, and postcool durations for
treatment algorithms for different tissue depths discussed herein,
including superficial, thin effect and deep tissue treatments.
FIG. 19 shows various duty cycles (e.g. on times) of cooling and
heating during the different phases of treatment. The figure
illustrates the specific duty cycles (e.g. on-times and interval
between on-times) of cooling and heating during the stages of
pre-cooling, energy delivery (heating) and post cooling. The
cooling and heating duty cycles can be controlled and dynamically
varied by an electronic control system known in the art.
Specifically the control system can be used to control the
electronic solenoid valve (described herein) for controlling the
flow of coolant and the RF generator supplying RF energy.
In various embodiments, the invention can include sensors to
measure parameters such as the skin surface temperature, the
interior or exterior temperature of the electrode structure, the
dielectric layer temperature, or the tissue temperature at a
selectable depth. Accordingly, sensors 20 can be positioned in the
interior or exterior of the electrode structure and adjacent
dielectric layer 32'. One or more sensors 20 can be coupled to
electronic control system 56 and can be used to control the
delivery of one or both energy and cooling to the skin and target
tissue, Suitable temperature sensors and sensor technologies
include thermocouples, thermistor, infared sensors/technology and
ultrasound sensors/technology. The latter two being well suited for
measuring temperature at tissue sites located down inside the
tissue as opposed to near or on the surface. Such sensors enable
the measurement and generation of temperature depth or
thermoprofile of the tissue. Such a thermoprofile could be used for
process control purposes to assure that the proper amounts of
heating and cooling were being delivered to achieve a desired
elevated deep tissue temperature while maintaining skin tissue
layers below a threshold temperature for thermal injury. The
physician would use the measured temperature profile to assure that
they were staying within the bound of an ideal/average profile for
a given type of treatment (e.g. sebaceous gland treatment).
In addition to the treatment methods discussed herein, in other
embodiments the invention can be configured for skin rejuvenation.
In these embodiments, the delivery of thermal energy to the target
tissue is controlled/reduce to only cause a wound healing response
and not necessarily collagen contraction. This would healing
response results by delivering thermal energy to the tissue to
induce a condition called fibroplasia. This is a condition in which
there is a proliferation or otherwise infiltration into the dermis
of a large number of fibroblast cells. These fibroblast cells in
turn, lay down or deposit collagen into or adjacent the thermal
affect zone causing the skin rejuvenation process. However by
delivering a selected amount of energy, a proportion of the
fibroblasts in the dermis can be killed off. As a result, a wound
healing response occurs, in which there is large infiltration of
fibroblasts into the dermis, with a large number of fibroblasts
present than before treatment. These new fibroblasts lay down new
collagen as part of a wound healing response and this rejuvenates
the skin. Thus by controlling the amount of thermal energy delivery
to the target tissue (and/or temperature of), the resulting tissue
affect can be titrated to produce skin rejuvenation for lower
levels of delivered energy, or collagen contraction configured to
tighten the skin for higher levels of delivered energy. If the
collagen contraction/skin tightening is positioned very
superficially, it can help to minimize the appearance of wrinkles.
If the area of collagen contraction is located deeper in the
dermis, it can tighten up areas of loose skin.
As discussed herein, various embodiments of the invention can
employ either mono-polar or bi-polar electrode implementations. One
bi-polar embodiment shown in FIG. 20 can comprise very dense arrays
of small electrodes 16 where every other electrode in the array is
an opposite pole of a bi-polar electrode pair. The electrode array
in this embodiment will produce a very superficial delivery of
thermal energy into the tissue extending from one bi-polar pair to
another. In contrast, a mono-polar electrode will produce a much
deeper tissue affect than will the bi-polar electrodes. This depth
difference in thermal affect between the two types of electrodes
results from the difference in current paths for mono-polar versus
bi-polar electrodes. For mono-polar electrode configurations, the
current flows from the positive electrode to a return electrode
located far away on the patient's body. In contrast for a bi-polar
electrode pair, all the current paths are localized between
electrode pairs located on the electrode array (e.g the energy
delivery device).
In various embodiments, different electrode configurations can be
employed for different targeted tissue layers or sites or for
different forms of treatment to the same site. For example, when
treating deeper target tissue layers (e.g. >100 .mu.m tissue
depth) such as the subcutaneous fat or the deep dermis, a
mono-polar electrode configuration could be selected for its
ability to delivery energy to the deeper tissue sites. In other
embodiments treating more superficial tissue layers (e.g. 100 .mu.m
tissue depth), for example wrinkle removal, a bi-polar electrode
configuration would be preferable. In various bi-polar electrode
embodiments, the depth of the thermal tissue affect is limited to
the more superficial tissue layers with little or no deep tissue
effect, even for longer periods of energy delivery. Accordingly,
various bi-polar embodiments can be readily configured for use with
continuous cooling system/apparatus either in the form of a
continuous spray or a circulating fluid. The use of continuous
cooling presents several advantages in that i) more conventional
and potentially less expensive cooling systems (e.g. water cooling,
air cooling and the like) can be employed, ii) the complexity of
the system or apparatus is reduced in that reduced hardware and
soft resources are required to control the delivery of coolant; and
iii) improved ease of use for the medical practitioner.
Many current dermatological procedures involving the delivery of
heat to tissue are done with lasers. However, the use of lasers for
dermatologic procedures has several technical drawbacks which limit
the access and depth of tissue treatment, reduce efficacy and cause
undesirable patient complications. First, laser light propagating
in tissue exhibits a phenomena known as scattering in which the
incident light is scattered by incident cells and tissue from its
original optical path. This scattering results in the incident
light beam no longer traveling in a straight, and hence,
predictable path within the target tissue. The scattering has the
further detrimental effect of causing nonuniform intensity within
the beam surface and hence a nonuniform thermal effect in the
tissue contacted by the beam. Specifically, the outer areas of the
laser beam undergo more scattering than the interior or more
central portions of the beam. This causes the central portions of
the beam to become more focused as the beam propagates deeper into
the tissue or in other words, the central portion becomes more
intense while the outer areas and beam edges less intense. This
nonuniform beam intensity can in turn lead to non-uniform heating
and tissue effects as the beam moves deeper into the tissue and
becomes increasingly focused on a smaller and smaller area. This
non-uniform intensity can readily cause a nonuniform cosmetic
effect. More importantly it may be significant enough to cause
severe thermal injury with related medical complications (e.g.
burning, damage or destruction of nerves, blood vessels, etc.).
Various mono-polar electrode embodiments of the present invention
provide improvements and features for overcoming these and other
limitations. They also provide the medical practitioner with an
apparatus generally better suited for treating the skin and
underlying tissue including the deeper dermal and subdermnal
tissue. These improvements/advantages include a more uniform
delivery of energy in the target tissue beneath the surface of the
electrode and dispersement of delivered energy outside the target
tissue site. This is attributed to i) the more uniform current
density of dielectric coated mono-polar electrodes and ii) the
tendency of current density (and hence energy density) in
mono-polar electrodes to diffuse (as opposed to becoming
concentrated) as it spreads out and travels through the body to the
return electrode, becoming negligible outside the tissue treatment
site. This actually has some advantages over other methods of
heating the tissue.
In various embodiments the bi-polar electrodes can comprise an
array of electrodes, including a highly dense array of electrodes.
As shown in FIG. 20, such an array can include a multiple bar
pattern of electrodes, where every other electrode of a sequence of
thin rectangular bars is an electrode of a bi-polar pair. In
embodiments where the electrodes are located very close to each
other tissue, thermal effects (e.g. treatment) tends to occur in
the tissue underlying gap between the electrodes. In various
embodiments the gap between electrodes of a bi-polar pair can
include but is not limited to a range from 0.0001 to 1 inch, with
specific embodiments of 0.001, 0.010, 0.025, 0.050, 0.1, 0.25 and
0.5 inches. As the distance between electrodes comprising a pair
increases, the electrodes begin to behave like mono-polar
electrodes. That is they are not influenced by the presence of
another electrode that may be in the same or other tissue treatment
area. In various embodiments, the electrode spacing or electrode
gap can be varied or modulated along one or more axis of an
electrode array. In one embodiment with a linear array of
rectangular electrode, the electrode gap can be controllably varied
in the longitudinal direction in order to tailor the resulting
pattern of thermal/tissue affect in the targeted tissue. Portions
of the linear array can have a very small electrode gap producing a
near continuous affect, while other portions can have a wider gap
producing discrete zones of thermal affect with adjacent
substantially untreated zones. In various embodiments an
intermediate electrode gap could be chosen to achieve both a
bi-polar and mono-polar effect in terms of depth and pattern of the
thermal effect. To avert any potential edge effects with bi-polar
electrodes, dielectric coating and capacitive coupling could be
used on bi-polar pairs as well as mono-polar pairs.
Another drawback of the use of lasers in dermatologic procedures
such as skin resurfacing is the fact that the procedure has to be
done in patchwork fashion. Specifically a small area of the face is
treated, approximately one square centimeter area, either with a
laser that has a beam that's that size, or a beam that has a
smaller beam diameter and some kind of a scanning mirror system
that would result in the beam moving over a one square centimeter
area. The nature of this procedure is a discrete or patchwork
delivery of energy/treatment to one small area at a. So one square
centimeter is treated and the laser is moved to next area.
Consequently, it is a very time consuming and arduous process. Also
it can result in the necessity of coming back for treatment
sessions in separate visits to the physician with the patient
having to undergo the undesirable side affect (e.g.. redness,
blistering, etc.) each time.
Using various embodiments of the invention discussed herein, a
similar discrete treatment method could employed. However the use
of cooling would prevent/reduce the occurrence of blistering and
burning. Specifically the apparatus may be used to treat one square
centimeter skin, using the spray cryogen to achieve a pre, inter or
post cooling affect as needed. After treating the fist area of skin
the electrode/device would be lifted off the surface the skin and
moved to the next area (e.g. square centimeter) of skin to be
treated with this procedure being repeated until the entire desired
target skin/tissue site was treated.
In alternative embodiments the procedure could be done in a
quasi-continuous or even a continuous fashion. One embodiment of
treatment method would involve a quasi-continuous pulsed method
where a short spray of pre-cooling is done, then a short
application of RF energy, followed by a short spray of post-cooling
and then a period of waiting where the physician observes the
physical appearance of the skin as well as monitoring the skin
and/or tissue temperature using sensor described herein. The
procedure is then repeated as needed until the entire desired
target site is treated.
In a related embodiment, the procedure could be done in an even
more continuous fashion with a painting or sliding motion of the
energy delivery device/electrode across the surface of the skin. In
these embodiments both cooling and heating application sequences
would be done in a more continuous fashion and the pulsing method
(e.g of cooling and heating) is one approach that lends itself to
that. In these embodiments, cycles of cooling, heating and cooling
could be done between five and ten times a second, or even faster.
The depth of the tissue effect could be increased with a longer RF
heating phase (which could be pulse or continuous) and if necessary
a longer period of precooling. The use of bi-polar electrode
configurations would be particularly well suited for continuous
treatment embodiments using continuous cooling and heating, since
the depth of current flow, and hence energy delivery, for bi-polar
configurations is limited. The ability to treat tissue in more
continuous fashions where the device/electrode is slid across the
surface of the skin is a distinct advantage over the use of laser
treatment used to treat discrete areas of skin in a patchwork
approach.
The continuous skin treatment methods (e.g. by sliding the
electrode) afforded by embodiments of the present invention would
be particularly advantageous/desirable to surgeons and other
physicians who typically use their hands during medical procedures
would rather have a instrument where they can have some control
over movement of the instrument. Moreover the apparatus of the
present invention presents the further advantage of allowing
physicians to utilize their surgical skills and manual dexterity to
achieve a finer and precise level of control over the delivery of
the treatment and hence the quality of the clinical outcome versus
laser devices that can only be used to treat skin in a
noncontinuous patchwork fashion. The use of more continuous
treatment with embodiments of the present invention could also
significantly shorten procedure times. Also if the physician wanted
to deliver more treatment in anyone spot he/she leaves the
electrode/device there a little bit longer. This allows the
physician to titrate the treatment effect in different areas of the
target tissue.
Another advantage of various embodiments of energy delivery devices
(e.g., dielectric-coated cryogen cooled electrodes) adapted to
slide over the skin and deliver RF energy in a near continuous
fashion is greater access to different areas of tissue where a
laser could not get easily get access or would otherwise be
obstructed. Such areas include parts of the body with pronounced
curvature, acute angles or otherwise rough and uneven surfaces.
In various embodiments of the invention, collagen-containing tissue
is treated by controllably delivering thermal and/or mechanical
energy through the epidermis to the collagen containing tissue so
as to change a physical feature or property of the epidermis
through the thermal modification of the collagen containing tissue.
In various embodiments, the physical feature can be one or more of
the following, a reduction in size of a wrinkle in the epidermis, a
reduction in an elastosis of the epidermis, an improvement of an
epidermis contour irregularity, a tightening of the epidermis,
remodeling of the underlying collagen containing tissue site,
remodeling of the epidermis, changes in three-dimensional
contouring, and combinations thereof.
The collagen containing tissue can be in a dermal layer, a deep
dermal layer, a subcutaneous layer underlying a dermal layer, in
fat tissue, and the like. Intracellular modification of the
epidermis and skin appendages can also be achieved. A reverse
thermal gradient, wherein the temperature of the epidermis is less
than a temperature of the collagen containing tissue, can be used
to create the composition of matter. With the reverse thermal
gradient, the surface temperature of the skin can be at, above or
below body temperature. When the composition of matter is created
there is controlled cell necrosis of the epidermis, the
collagen.
As used in the application "in vivo" refers to the thermal,
mechanical and/or magnetic modification of tissue within a living
composition of matter.
An aesthetic composition of modified living matter is a composite
three dimensional phenotype that is comprised of a remodeled
preexisting cutaneous container of preexisting soft tissue
contents. The aesthetic composition of matter can include combined
remodeling of the soft tissue contents and its container. Matrix
interactions of collagen with energy involve native or preexisting
collagen and/or the de novo production of nascent collagen by the
induction of the wound healing sequence. These interactions are
produced by the molecular and cellular remodeling of the collagen
matrix. Molecular remodeling of the extracellular matrix occurs
from the contraction and distraction of preexisting collagen
fibrils. Cellular remodeling of the matrix is a delayed phenomenon
and involves the activation of a wound healing sequence with
fibroblast contraction and nascent collagen production as a static
supporting structure of the remodeled matrix.
Electromagnetic and mechanical modalities are used to remodel the
matrix and to alter intracellular metabolism. These modalities may
be applied separately or in a coupled device geometry. Coupled
mechanical force reduces the energy requirement to create a
specific morphological result and is typically applied
externally.
For many aesthetic applications, contact with the skin by the
energy source is required. An alternating electrical current may be
used to remodel the extracellular collagen matrix of the dermis and
subcutaneous tissue. However, weaker magnetic fields can also be
employed to delicately modify the intracellular metabolism of these
structures including the epidermis and skin appendages. More rapid
phenotypic changes can occur from electrical remodeling of the
extracellular matrix than magnetic modification of intracellular
processes of the epidermis and skin appendages. Rather than
producing observable changes, magnetic modification may also be
used for maintenance or homeostasis of the aesthetic phenotype.
The visual perception of animate matter is due to a composite
electromagnetic field of component atoms in various soft tissue
structures. The human perception of animated matter is also
determined and restricted by the limited span of the visual
spectrum in comparison to the entire electromagnetic spectrum.
Methods of detecting the electromagnetic field (EMF) of animate
matter by using a larger electromagnetic (EM) spectrum (than the
visual spectrum) can provide a delineation of EMF patterns not
typically seen by the human eye. Changes in this broader EM
spectrum may be detected before they become visually apparent. The
pattern of change in the EMF may be used as a diagnostic modality
before phenotypic changes of aging occur in tissue. These
previously non-visualized changes in the EMF of individuals may
provide an early warning signal before these changes become
morphologically apparent. Furthermore, manipulation of the EMF
pattern to a more youthful EMF profile may provide the means to
limit or reverse the morphological expression of this aging
process.
Ablative methods include non invasive and minimally invasive
removal of subcutaneous fat in addition to resurfacing of the skin.
Non-ablative methodologies remodel skin and soft tissue with a
minimum of cellular and extracellular necrosis. Both ablative and
non-ablative methodologies are used to create an aesthetic
composition of matter (ACM).
Depending upon the type of aesthetic composition of matter to be
formed, a treatment modality matrix is created to determine the
most effective combination of electromagnetic energy, mechanical
force, method of application (ablative or non ablative) and tissue
interaction (molecular vs. cellular remodeling). However, central
to this matrix is the use of an energy source, including but not
limited to electromagnetic energy, to alter the extracellular
collagen matrix and intracellular metabolism of the epidermis and
skin appendages with a minimum of collateral damage to tissues that
do not require modification. Complimentary application of
mechanical force can be used to lower electromagnetic energy
requirements and potential side effects of treatment. The pattern
of thermal energy delivery is no longer a random Brownian process.
Instead, energy delivery becomes a directed process that produces a
specific morphological effect without collateral tissue damage.
Ablation is avoided entirely or it is created selectively to limit
thermal side effects in creation of the composition of matter. As a
result, an aesthetic composition of modified living matter is
reliably created that is either an entire phenotype or a
constituent component of a whole.
Vectors of external mechanical compression can be used to smooth
surface wrinkling by conforming dermal defects within a preheated
collagen matrix of the collagen containing tissue site. A partial
phase transition of a matrix can be created at a lower temperature.
As a result, the clinical effectiveness is enhanced while side
effects of treatment are concomitantly reduced.
A more in-depth description of skin anatomy is required to
understand the interaction of energy with its component parts. The
epidermis is the cutaneous barrier to the outside world and is
provided by the keratin bilipid layer of the stratum corneum which
is produced by the continuing upward maturation of keratinocytes
within the epidermis. Thermal and biological components of the skin
barrier are created from this maturation process. The solar or
ultraviolet component of the barrier is provided by melanocytes
that reside in basilar layer of the epidermis. Melanin granules are
produced in these cells which are then distributed to upwardly
migrating keratinocytes by dendritic extensions of the cell
membrane. An additional population of melanocytes and keratinocytes
is also present in the skin appendages. These structures are the
hair follicles, sebaceous and sweat glands which are present in the
deeper dermal and subdermal levels. The dermis is the main
structural support of the skin and is immediately subjacent to the
epidermis. This supporting layer is mainly comprised of collagen
fibrils that are subdivided into papillary and reticular component.
The more superficial papillary dermis is immediately subjacent to
the epidermis and is less dense than the deeper reticular
dermis.
Burns are the morphological result of thermal energy interactions
with skin and are classified into first, second and third degrees
on the basis of dermal depth. A first-degree burn is a thermal
injury that extends superficially into the epidermis and does not
involve blistering or ablation of the skin. A temporary erythema of
the skin occurs that resolves within twenty-four hours. A healing
or reepithelialization process is not required. A second degree
burn is a deeper thermal injury that extends into the dermis for a
variable depth and is characterized by blistering and crusting.
Ablation of the epidermis occurs with destruction of the dermis at
either a superficial or deeper level. Superficial second-degree
burns extend into the papillary dermis and are readily heal by
reepithelialization because the skin appendages are not destroyed.
For deeper second degree burns, a greater portion of the dermis is
ablated which may complicate healing and reepithelialization. With
a deep second degree burn, many of the skin appendages are
destroyed in addition to the loss of normal dermal
architecture.
Thinning and disruption of normal dermal anatomy can permanently
alter the texture and elasticity of the skin. For many of these
burn patients, a plastic or translucent appearance of their face is
apparent. Obviously, a thinner margin of safety is present in deep
second degree burns. For this reason, deeper second-degree burns
are more frequently converted to burn scar deformities than more
superficial burns. A third degree burn is characterized by the full
thickness destruction or ablation of all skin layers including the
skin appendages. Healing by reepithelialization does not occur
normally but is achieved by the lengthy healing process of
secondary intention. Unless surgically closed the burn wound can
form granulation tissue that slowly contracts to close the open
rent in the biological barrier. Excessive scarring and deformity is
likely. A thin scar epithelium is typically formed over the burn
scar. This fragile biological barrier is easily disrupted with
minor trauma. Repeated ulceration of the burn scar may even require
subsequent revisional surgery.
Aging of the skin can also be classified in a manner similar to
thermal burns. Wrinkling is mainly caused by depletion of collagen
matrix in the papillary dermis. This intradermal or second-degree
deficit is a more superficial contour deformity than glabellar or
nasolabial creases which are full thickness dermal defects that
extend through the entire papillary and reticular dermis.
Resurfacing of the skin can also be classified in a manner similar
to thermal burns. After ablation of the epidermis, skin appendages
play a central role in the reepithelialization process. Skin
appendages are present in different densities depending upon the
specific area of the body. The highest density is present in the
fascial skin where current laser modalities of resurfacing are
practiced. Skin appendage density in other areas such as the neck,
trunk and extremities is inadequate to provide a consistent pattern
of reepithelialization. The skin appendages, consisting of hair
follicles and sebaceous glands, contain keratinocytes and
melanocyte that are the crucial components of reepithelialization.
Diminution in either cell population has significant ramifications
in the reestablishment of a functional epidermal barrier. With
deeper second degree resurfacing, there is also an increased risk
that treated areas can be more easily converted to a third-degree
burn if the reepithelialization process is protracted or if this
process is complicated with infection.
Following reepithelialization, a four to eight month period of burn
wound maturation ensues that is characterized by hyperemia and
transparency in which the skin appears shinny and pink. Thinning of
the remodeled dermis produces a porcelain texture of the skin that
is similar to the faces of many burn patients. Although wrinkling
is diminished, this alteration of normal skin texture remains a
permanent feature of a patient's face.
The use of a conformance-energy delivery device offers benefits of
enhanced clinical outcomes and a reduction of treatment side
effects. Enhanced clinical outcomes include a greater effectiveness
to correct superficial and deep wrinkling of facial skin. Duration
and pain during the healing period are significantly reduced as the
level of resurfacing is more superficial. A conformance-energy
delivery device can be safely applied to areas outside the face
because the depth of dermal ablation has been minimized without
loss of clinical effectiveness. Skin tightening of treatment areas
is also provided while simultaneously correcting surface
irregularities.
With an appropriately shaped energy delivery surface, the ability
exists to shape the skin envelope into a desired three dimensional
contour. These benefits are possible while minimizing surface
ablation. Use of the conformance-energy delivery device reduces
side effects by lowering the amount of thermal energy needed to
resurface a treatment area. With this device, superficial
resurfacing is capable of achieving deeper thermal effects. Healing
from a superficial second degree resurfacing reduces the
depigmentation and texture changes that are more common with deep
second degree resurfacing. A prolonged period of erythema is
avoided. Instead of an operating room, patients can be treated in
an office setting without the occupational risks of a laser.
With the composition of modified living matter of the present
invention, a matrix of different operational modes can be used to
create different tissue effects. A "pressing" or stationary mode of
application with convection cooling can conform the skin surface
with minimal ablation. In this instance, wrinkles and creases are
treated by selectively heating and conforming the dermis. Skin
tightening without ablation is also performed in this particular
mode of application.
A different mode of application is used to treat sun damaged skin
or residual wrinkling that is not corrected by non-ablative
applications. The device is applied in a mobile fashion similar to
"ironing" a shirt. Mobile compression without convection cooling
creates the present composition of matter resulting in a
resurfacing of the skin and application of shearing vectors of
force that additionally smooth the matrix.
A matrix of different modes of application can be created depending
upon the clinical circumstances. For example, a cold iron
(convection cooling with shearing and compression) may be ideal in
conditions that require maximal smoothing of surface contour
without ablation. This mode of application provides the greatest
benefit in the hip and thigh areas where contour irregularities of
cellulite are severe but solar damage is minimal. Patients with
severe wrinkling of the face without solar damage may also benefit
from this particular permutation.
The creation of the composition of modified living matter of the
present invention can employ the creation of a reverse thermal
gradient and involve other strategies to avoid the blistering of
skin. Hydration facilitates the passage of an electrical current
through the epidermis by reducing surface impedance. Another
significant effect is the increase in thermal conductance of the
stratum corneum. Tissue components such as the keratin/lipid
bilayer of the stratum corneum are poor thermal conductors and
function as thermal insulators to preserve the overall heat content
of the patient. Hydrated stratum corneum is a better thermal
conductor which promotes heat transfer to underlying collagen
containing tissues. The collagen containing dermis that has not
been hydrated can behave as a thermal insulator as well as an
electrical resistor. As a result, the thermal content of the target
collagen containing tissue is increased selectively.
Energy delivered to the soft tissue system, defined by the collagen
containing tissue site, remodels the collagen matrix by disrupting
the intermolecular crosslinks within the fibril. Although
temperature is a measure of heat content, an accurate measure of
energy delivery to the tissue is required. Measure of dose rate and
overall dose to the tissue is required to determine the most
effective control parameters. Dose rate is important due to the
time dependence of thermal conduction, thermal convection and
relaxation processes. Total dose is also important as there are a
known number of molecules to be contracted with a required amount
of energy per molecule. Another factor that affects the heat
content of tissue is the thermal dissipation that occurs through
thermal conduction away from the target tissue and the thermal
convection from vascular and surface structures.
In contrast to the application of energy, manipulation of energy
losses to the collagen containing tissue underlying the epidermis
provides another means to avoid surface ablation. Thermal
conduction losses occur through the passive dissipation of heat
through tissue and is limited by local tissue parameters. In
contrast, convective heat transfer occurs through the physical
movement of heated matter away from the target tissue and is a
process that can be actively manipulated. Sequential flash cycles
of surface cooling and tissue heating provides a reverse thermal
gradient as the heat dissipated from surface convection occurs
faster than subdermal tissues. Cycles of surface cooling and tissue
heating are performed with a thermal energy source. A progressive
increase in the subdermal heat content occurs while maintaining a
constant surface temperature. This occurs because the removal of
heat by surface convection is more rapid than thermal conduction
within the dermis. Other approaches to reduce the thermal load to
the skin surface can be employed. Multiple port focusing with
ultrasound in a tandem fashion can have a similar effect of
dispersing energy. A combination of these modalities may be
employed to avoid thermal damage to the epidermis.
Additionally, in creating the composition of the present invention,
the stability of the collagen triple helix can be chemically
altered prior to thermal denaturization. The collagen shrinkage
temperature (Ts) is an indication of molecular stability and is
determined by the amount of cross linkage. Reagents such as
hyaluronidase (Wydase) that enzymatically decrease fiber stability
can reduce the shrinkage temperature (Ts). Typically, a reduction
of 10 C. in the Ts is obtained by the injection of this reagent. As
a result, power requirements to target collagen containing tissues
are reduced. The solution can be combined with a dilute local
anesthetic and injected into target tissues with the "tumescent"
technique.
Thermal shrinkage, or tightening of the underlying collagen
containing tissue can be provided without the destruction of the
overlying epidermis. This process of molecular contraction has an
immediate biophysical effect upon the matrix and is based upon the
cleavage cascade of intramolecular and intermolecular bonds within
the collagen fibril. Skin tightening with thermal contraction and
remodeling of collagen can correct areas such as the thighs, knees,
arms, back and hips without unsightly scarring of standard
techniques. Areas previously corrected by surgical procedures, such
as face and neck lifts, could also be corrected without requiring
surgery or the typical incisions around the ear. Elastosis, or
stretching of the abdominal skin from pregnancy, can be corrected
without the long scar commonly associated with an abdominoplasty.
Thermal remodeling of underlying collagen containing tissues is
effective, non-invasive alternative for the aesthetic treatment of
these areas.
Treatment of "cellulite" of the thighs and hips is another example.
Typically, the subcutaneous fat layers have loculations from
fibrous septae that contain collagen. These fibrous septac call be
remodeled to tighten the soft tissue in areas such as the hips and
thighs. Additionally, dermal and subdermal telangiectasias (spider
veins) are diminished by the contraction of the matrix adjacent to
these vessels.
Another component of electromagnetic remodeling is cellular
remodeling of collagen containing tissues with a
thermal-conformance device. The use of low level thermal treatments
over several days provides an additional way to contract skin
without blistering. The cellular contraction process is initiated
and involves the inflammatory/wound healing sequence that is
perpetuated over several days with sequential and lengthy low level
thermal treatments. This cellular contraction process is a
biological threshold event that is initiated by the degranulation
of the mast cell that releases histamine which initiates the
inflammatory wound healing sequence. Histamine alters endothelial
permeability and allows the creation of inflammatory edema. In this
tissue system, contraction of skin is achieved through fibroblastic
multiplication and contraction with the deposition of a static
supporting matrix of nascent scar collagen. The nascent matrix is
simultaneously remodeled with a conformance template that is
incorporated in the thermal energy delivery device. For many
aesthetic and functional applications, molecular and cellular
effects occur in tandem with each other.
With the application of a conformance template, surface
irregularities with depressions and elevations have vectors
directed to the lowest point of the deformity. Prominent "pores" or
acne scarring of the skin have a similar pattern to cellulite but
on a smaller scale that can also be corrected. The application of
pressure reduces the power required to remodel the matrix and
should diminish surface ablation. Compression can also exert
electrical impedance and thermal conductivity effects that can
allow delineation within different components of collagen
containing tissues.
Aesthetic conformers with a thermal energy source can also be used
to remodel the subcutaneous fat of hips and thighs in addition to
the tightening of the skin envelope. Digital capture of a
preexisting aged contour is used to digitally form an aesthetic
three dimensional contour that subsequently provides the means to
fabricate a conformance template. Additional aesthetic applications
include congenital prominence of the ear in which the convolutions
(antehelical fold) are altered by remodeling the collagen within
the cartilage. The nasal tip can be conformed to a more
aesthetically pleasing contour without surgery.
A conforming aesthetic template can be used with any process that
remodels underlying collagen containing tissue. In addition to the
thermal remodeling of collagen, chemical modalities that invoke the
wound healing sequence can be combined with a conforming esthetic
template. Glycolic acid can induce a low level inflammatory
reaction of the skin. Scar collagen and fibroblastic (cellular
contraction) are directed by converging and diverging vectors
created from a conformer that smooths and tightens the skin
envelope into a more desirable contour. Additionally, a softer and
more compliant skin texture in achieved.
Referring to FIG. 21, in an embodiment, skin treatment apparatus 10
can be coupled to an open or closed loop feedback system/resources
60. As shown in FIG. 21, feedback system 60 couples sensor 346 to
power source 392. For purposes of illustration, energy delivery
device 314 is one or more RF electrodes 314 and power source 392 is
an RF generator, however all other energy delivery devices and
power sources discussed herein are equally applicable.
The temperature of the tissue, or of RF electrode 314 is monitored,
and the output power of energy source 392 adjusted accordingly. The
physician can, if desired, override the closed or open loop system.
A controller 394 or microprocessor 394 can be included and
incorporated in the closed or open loop system 60 to switch power
on and off, as well as modulate the power. The closed loop system
utilizes microprocessor 394 to serve as a controller to monitor the
temperature, adjust the RF power, analyze the result, refeed the
result, and then modulate the power. More specifically, controller
394 governs the power levels, cycles, and duration that the radio
frequency energy is distributed to the individual electrodes 314 to
achieve and maintain power levels appropriate to achieve the
desired treatment objectives and clinical endpoints. Controller 394
can also in tandem, govern the delivery of cooling fluid.
Controller 394 can be integral to or otherwise coupled to power
source 392 and can also be coupled to a fluid delivery apparatus.
In one embodiment controller 394 is an Intel.RTM. Pentium.RTM.
microprocessor, however it will be appreciated that any suitable
microprocessor or general purpose digital or analog computer can be
used to perform one or more of the functions of controller 394
stated herein.
With the use of sensor 346 and feedback control system 60 skin or
other tissue adjacent to RF electrode 314 can be maintained at a
desired temperature for a selected period of time without causing a
shut down of the power circuit to electrode 314 due to the
development of excessive electrical impedance at electrode 314 or
adjacent tissue. Each RF electrode 314 is connected to resources
which generate an independent output. The output maintains a
selected energy at RF electrode 314 for a selected length of
time.
Current delivered through RF electrode 314 is measured by current
sensor 396. Voltage is measured by voltage sensor 398. Impedance
and power are then calculated at power and impedance calculation
device 400. These values can then be displayed at user interface
and display 402. Signals representative of power and impedance
values are received by a controller 404.
A control signal is generated by controller 404 that is
proportional to the difference between an actual measured value,
and a desired value. The control signal is used by power circuits
406 to adjust the power output in an appropriate amount in order to
maintain the desired power delivered at respective RF electrodes
314.
In a similar manner, temperatures detected at sensor 346 provide
feedback for maintaining a selected power. Temperature at sensor
346 is used as a safety means to interrupt the delivery of energy
when maximum pre-set temperatures are exceeded. The actual
temperatures are measured at temperature measurement device 408,
and the temperatures are displayed at user interface and display
402. A control signal is generated by controller 404 that is
proportional to the difference between an actual measured
temperature and a desired temperature. The control signal is used
by power circuits 406 to adjust the power output in an appropriate
amount in order to maintain the desired temperature delivered at
the sensor 346. A multiplexer can be included to measure current,
voltage and temperature at sensor 346. Energy can be delivered to
RF electrode 314 in monopolar or bipolar fashion.
Controller 404 can be an analog or digital controller, or a
computer with driven by control software. When controller 404 is a
computer it can include a CPU coupled through a system bus. On the
system can be a keyboard, disk drive, or other non-volatile memory
systems, a display, and other peripherals, as are well known in the
art. Also coupled to the bus are a program memory and a data
memory. Also, controller 404 can be coupled to imaging systems
including, but not limited to, ultrasound, thermal and impedance
monitors.
The output of current sensor 396 and voltage sensor 398 are used by
controller 404 to maintain a selected power level at RF electrode
314. The amount of RF energy delivered controls the amount of
power. A profile of the power delivered to electrode 314 can be
incorporated in controller 404 and a preset amount of energy to be
delivered may also be profiled.
Circuitry, software and feedback to controller 404 result in
process control, the maintenance of the selected power setting
which is independent of changes in voltage or current, and is used
to change the following process variables: (i) the selected power
setting, (ii) the duty cycle (e.g., on-off time), (iii) bipolar or
monopolar energy delivery; and, (iv) fluid delivery, including flow
rate and pressure. These process variables are controlled and
varied, while maintaining the desired delivery of power independent
of changes in voltage or current, based on temperatures monitored
at sensor 346.
Referring now to FIG. 22, current sensor 396 and voltage sensor 398
are connected to the input of an analog amplifier 410. Analog
amplifier 410 can be a conventional differential amplifier circuit
for use with sensor 346. The output of analog amplifier 410 is
sequentially connected by an analog multiplexer 412 to the input of
A/D converter 414. The output of analog amplifier 410 is a voltage
which represents the respective sensed temperatures. Digitized
amplifier output voltages are supplied by A/D converter 414 to
microprocessor 394.
Microprocessor 394 sequentially receives and stores digital
representations of impedance and temperature. Each digital value
received by microprocessor 394 corresponds to different
temperatures and impedances. Calculated power and impedance values
can be indicated on user interface and display 402. Alternatively,
or in addition to the numerical indication of power or impedance,
calculated impedance and power values can be compared by
microprocessor 394 to power and impedance limits. When the values
exceed predetermined power or impedance values, a warning can be
given on user interface and display 402, and additionally, the
delivery of RF energy can be reduced, modified or interrupted. A
control signal from microprocessor 394 can modify the power level
supplied by energy source 392.
FIG. 23 illustrates a block diagram of a temperature and impedance
feedback system that can be used to control the delivery of energy
to tissue site 416 by energy source 392 and the delivery of cooling
solution 48 to electrode 314 and/or tissue site 416 by flow
regulator 418. Energy is delivered to RF electrode 314 by energy
source 392, and applied to tissue site 416. A monitor 420
ascertains tissue impedance, based on the energy delivered to
tissue, and compares the measured impedance value to a set value.
If the measured impedance exceeds the set value, a disabling signal
422 is transmitted to energy source 392, ceasing further delivery
of energy to RF electrode 314. If the measured impedance is within
acceptable limits, energy continues to be applied to the
tissue.
The control of the flow of cooling solution 48 to electrode 314
and/or tissue site 416 is done in the following manner. During the
application of energy, temperature measurement device 408 measures
the temperature of tissue site 416 and/or RF electrode 314. A
comparator 424 receives a signal representative of the measured
temperature and compares this value to a pre-set signal
representative of the desired temperature. If the tissue
temperature is too high, comparator 424 sends a signal to a flow
regulator 418 (which can be intergral to a pump 418) representing a
need for an increased cooling solution flow rate. If the measured
temperature has not exceeded the desired temperature, comparator
424 sends a signal to flow regulator 418 to maintain the cooling
solution flow rate at its existing level.
The foregoing description of a preferred embodiment of the
invention hag been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obviously, many
modifications and variations will be apparent to practitioners
skilled in this art. It is intended that the scope of the invention
be defined by the following claims and their equivalents.
* * * * *